1. Field of the Invention
The invention relates to a method of annunciating a user that a mobile telephone is located out of a service area, and a mobile telephone having a function of doing the same, and more particularly to a method of annunciating a user that a mobile telephone is not capable of making communication, because the mobile telephone is located out of a service area, and a mobile telephone having a function of doing the same.
Herein, a term “a mobile telephone” includes a portable phone, an automobile phone, a cellular phone, a phone having functions of a codeless phone and a cellular phone, used in personal handy phone system (PHS), and other similar phones.
2. Description of the Related Art
Various methods have been suggested to annunciate a user of a mobile telephone that the mobile telephone cannot make communication with other mobile telephones, when the mobile telephone is in a stand-by mode where the mobile telephone is waiting receiving radio signals from a base station, because the mobile telephone is located out of a service area.
For instance, Japanese Patent No. 2,870,077 has suggested a method of annunciating a user that a mobile telephone is located out of a service area, including the step of displaying an indicator such as an icon on a display screen which indicator indicates that the mobile telephone is located out of a service area.
In this method, a user cannot realize that he/she or a mobile telephone is located out of a service area unless he/she looks at the display screen. Hence, the method is accompanied with a problem that if he/she forgets having a mobile telephone with him/her and makes an appointment to meet somebody at a place located out of a service area, somebody cannot make communication with his/her mobile telephone, if somebody wants to change a place at which they are to meet each other.
In addition, the method is accompanied with another problem due to the fact that a user cannot realize that he/she or a mobile telephone is located out of a service area unless he/she looks at the display screen. Even if a user realizes that he/she has a mobile telephone with him/her, he/she may not realize that he/she or the mobile telephone moves out of a service area, when the mobile telephone is put in a bag. In such a case, somebody having an appointment with him/her to meet each other cannot make communication with him/her.
Japanese Unexamined Patent Publication No. 7-87010 has suggested a battery saving circuit to be used in a mobile telephone. The circuit judges that a mobile telephone is located within a service area, if the circuit can detect a control signal transmitted from a base station, and that a mobile telephone is located out of a service area, if the circuit cannot detect the control signal.
Japanese Unexamined Patent Publication No. 10-13330 has suggested a battery saving circuit to be used in a mobile telephone. In this circuit, a field intensity of a radio signal transmitted from a base station is compared to a threshold intensity to thereby judge whether a mobile telephone is located within a service area or out of a service area.
Japanese Unexamined Patent Publication No. 6-311101 has suggested a portable wireless phone including first means for judging whether a phone is located within a service area, and timers which switch a period of time between a first period of time including a turn-on period and a turn-off period in accordance with an output signal transmitted from the first means, and a second period of time including a turn-off period longer than the first period of time. When the portable wireless telephone is located within a service area, while the telephone is in a stand-by mode, a power supply supplying power to a signal receiver is controlled at the first period of time, and when the portable wireless telephone is located out of a service area, the power supply is controlled at the second period of time.
Japanese Unexamined Patent Publication No. 11-41168 has suggested a mobile telephone. A power supply is turned off when the mobile telephone is located within a service area. When a predetermined period of time has passed after the power supply was turned off, the power supply is automatically turned on. This ensures that a lifetime of a battery is lengthened.
However, the above-mentioned problems remain unsolved even in the mobile telephones suggested in the above-mentioned Publications.